The technical field of the invention is computer and communication systems having bus systems based either on parallel wired connections or on parallel optical links, such as laser diode arrays connected to corresponding photodiode arrays by one or more optical fibers.
Failure of a single channel may occur due to a disruption of the signal line, due to a short circuit along the line, or the like. In an optical bus, one of the light emitting devices, for example a laser diode, or one of the light detecting device may cease to operate. Also, the transmitting fiber can break or its transmission properties can otherwise be deteriorated. The likelihood of bus failures increases with the number of connected devices and corresponding signal lines.
It is known that any probable interruption of the data transmission due to faulty channels can be met by providing additional channels which take the place of those channels which are not transmitting properly. As the rerouting of the data through a redundant channel only occurs when one of the default channels fails, the technique is known as dynamic-redundancy technique.
This technique comprises two mechanisms: one for detecting the faulty channel; and another to relocate the data flow through one of the redundant channels.
Depending on the cause of the failure, the faulty channel may be recognized at the transmitting and receiving end of the bus simultaneously, for example if a laser diode or another transmitting component is identified as faulty, or only at the receiving end. In the latter case, the failure has to be reported back to the transmitting end of the bus. However, such methods are known to a person skilled in the art and are not the concern of this invention.
The invention relates to the fault-masking mechanism of the dynamic-redundancy technique, i.e. the routing of the data flow through one of the redundant channels.
Routing techniques as such are also widely known in the various fields of data transmission. For example, cascaded switch architectures like Batchef-Banyan soding circuits are used to direct data into the channels identified by a destination address carried by the transmitted data. In SU-A-1249503 (Derwent Abstract) and SU-A-553619 (Derwent Abstract) other techniques to avoid faulty channels are described.
It is an object of the invention to provide a cost-effective device rerouting the data flow from a faulty channel to a redundant channel. More specifically, the device should be suitable for high-speed applications, especially for optical bus systems. The new device should further consists of only a minimal number of gates as such gates cause a delay of the data transfer.